Polymethyl methacrylate (PMMA) is one of the polymerizates of methyl methacrylate. In the cosmetic field, PMMA has been used widely for production of fundamental cosmetics and makeup cosmetics by virtue of its matte feeling of use and high oil absorption. Particularly, since powder including PMMA has excellent sebum adsorption ability, it has been used widely for fundamental cosmetics for controlling sebum and makeup cosmetic products for amending a skin tone. In addition, an effect of amending a skin tone can be expected by virtue of a soft focusing effect derived from scattered reflection of light. It is known that such powder has a porous structure in order to realize the above-mentioned effects.
Many patents have been published to date about technologies of supporting a sunscreen by using porous or hollow particles. According to such technologies, an organic sunscreen is supported by dipping porous or hollow particles in the organic sunscreen.
Particularly, Korean Patent Publication No. 1261784 discloses a method for forming a composite pigment phase by mixing porous spherical PMMA with ethylhexyl methoxycinnamate with a high-speed mixer (title: ‘Organic Sunscreen-Supported Functional PMMA Composite Pigment, Method for Preparing The Same and Sunscreen Cosmetic Composition Including The Same). However, when an organic sunscreen is supported with and enclosed in a porous polymer, the organic sunscreen may be absorbed into the skin to cause skin irritation and a product formed through photoreaction may cause skin irritation. In addition, an organic sunscreen has low photostability, and thus there is a disadvantage in that it should be applied repeatedly with the lapse of time. In addition, Korean Patent Publication No. 0378521 (title: The method for preparation of sun protecting complex powder’) relates to a technology of coating and incorporating titanium oxide to the inner/outer part of powder by activating the inner/outer part of powder with an acid, and hydrolyzing titanium alkoxide at the inner/outer part of powder in situ. However, in this case, a strong acid, such as nitric acid or hydrochloric acid, is used to form OH groups in the inner/outer part of powder and TiO2 is synthesized directly by using a sol-gel process through heating at high temperature. Thus, such a condition using a strong acid and high temperature may cause a safety-related problem undesirably when using the composite powder is used as a cosmetic material.
Moreover, although an inorganic material, such as titanium oxide (TiO2) or zinc oxide (ZnO), used as a conventional inorganic sunscreen material has an excellent sunscreen effect, it has high polarity and large specific gravity and has a problem of agglomeration and precipitation in a formulation, and thus shows a limitation in that it causes a white turbidity and undergoes degradation of its unique excellent sunscreen effect. To solve the above-mentioned problems, a study has been conducted to enclose an inorganic material, such as titanium oxide or zinc oxide, in PMMA microspheres (Colloid Polym Sci, 2002, 280, 584-588). However, since such a structure does not have a porous structure contributing to reduction of specific gravity significantly, there is a limitation in that reduction of specific gravity cannot be accomplished while a number of inorganic material particles are agglomerated in the microspheres.
Under these circumstances, the inventors of the present invention have attempted a method which includes preparing porous PMMA microspheres first and then coating TiO2 nanoparticles to the surface of the voids by using polyphenol, in order to solve the above-mentioned problems. In general, it is known that polyphenol is contained in foods, such as wine, chocolate, tea leaves and persimmon, and is able of absorbing UV light. It is also reported that polyphenol can form a strong bonding with a metal ion (Science 2013 341:154). Although a patent (KR10-2010-0025762) and article (Chem. Mater., 2014, 26, 1645-1653) about coating technologies using polyphenol and a nanometal based on the above-mentioned characteristics were published, they are not directed to coating the voids of a porous structure capable of scattering light with an inorganic material as disclosed herein, and they are not intended to be applied to cosmetics requiring low specific gravity and high dispersion stability on the basis of an improved sunscreen effect of an organic/inorganic composite material of polyphenol and titanium dioxide.
The inventors of the present invention have developed a method for coating the voids and surface of a porous polymer support having excellent dispersibility with TiO2 nanoparticles and polyphenol in a multi-layer form, in order to overcome the problems of the related art. When using the method, it is possible to incorporate materials that can be bound with polyphenol simultaneously into a porous support, besides TiO2 nanoparticles. In addition, the inventors of the present invention have developed a novel sunscreen material having excellent dispersibility and an improved sunscreen effect by using the porous polymer microspheres coated with TiO2 nanoparticles and polyphenol. Since the composite is coated uniformly with the inorganic sunscreen in the material, there is little agglomeration of the inorganic sunscreen so that the sunscreen effect may be improved, and there is an advantage in that the material is safer in terms of skin irritation as compared to a polymer including an organic sunscreen. In addition, there is an advantage in that the content of TiO2 nanoparticles and that of polyphenol can be controlled with ease depending on number of coating times.
After the inventors of the present invention have conducted many studies to overcome the above-mentioned problems according to the related art, we have found that when porous organic/inorganic composite powder is prepared by repeating steps of attaching polyphenol to porous polymethyl methacrylate (PMMA) microspheres and attaching inorganic oxide nanoparticles to the porous polymethyl methacrylate (PMMA) microspheres to which polyphenol is attached so that inorganic oxide nanoparticles may be attached in a multi-layer form, it is possible to obtain porous organic/inorganic composite powder including an inorganic material attached uniformly on the surface of a porous organic polymer support. We have also found that when the porous organic/inorganic composite powder prepared from the above-mentioned method is applied to sunscreen cosmetics, it is possible to attach the inorganic particles used as a sunscreen uniformly to the support and to prevent agglomeration of the particles, and thus the inorganic sunscreen is allowed to maintain their unique excellent characteristics and provides an excellent sunscreen effect. The present invention is based on these findings.